Swollen feet happen when fluid leaks out of tiny blood vessels and collects in the tissues of your lower extremities. Gravity pulls that fluid downward throughout the day, which is why feet and ankles are almost always the first place swelling shows up. The causes range from something as simple as sitting too long to serious conditions involving the heart, kidneys, or blood vessels.
How Fluid Ends Up in Your Feet
Your body constantly moves fluid between your bloodstream and the surrounding tissues. Two opposing forces keep this in balance: pressure inside your blood vessels pushes fluid out, while proteins in your blood (especially one called albumin) pull fluid back in. Your lymphatic system acts as a cleanup crew, draining whatever excess fluid slips through.
Swelling occurs when any part of this system breaks down. That can mean too much pressure forcing fluid out, too little protein pulling it back, leaky vessel walls letting fluid escape more easily, or a sluggish lymphatic system failing to clear the excess. On top of that, your kidneys respond to many of these disruptions by holding onto extra salt and water, which makes the swelling worse.
Sitting or Standing Too Long
If you spend hours at a desk or on your feet without moving much, your calf muscles never get the chance to pump blood back up toward your heart. Blood pools in your lower legs, pressure builds in those small vessels, and fluid seeps into the surrounding tissue. This is the most common reason otherwise healthy people notice puffy feet at the end of the day.
Even brief movement makes a measurable difference. One study found that alternating between sitting and standing for just one minute at a time during a 20-minute period was enough to prevent lower leg swelling compared to staying in one position. You don’t need a workout. Walking to the kitchen, shifting positions, or doing a few calf raises at your desk can keep fluid from settling.
Venous Insufficiency
Your leg veins contain one-way valves that push blood upward toward the heart and stop it from falling back down. When those valves weaken or fail, blood flows backward and pools in the lower legs, a condition called chronic venous insufficiency. It’s one of the most common causes of persistent foot and ankle swelling, especially in older adults.
The hallmark is swelling that worsens as the day goes on and improves overnight. Over time, you may also notice visible veins near the skin’s surface, skin discoloration around the ankles, or a heavy, aching feeling in your legs. Left unmanaged, the sustained pressure can damage the tiny blood vessels in your skin and lead to chronic wounds.
Heart, Kidney, and Liver Disease
Swollen feet can be an early visible sign of organ problems happening deeper in the body.
In congestive heart failure, the heart can no longer pump blood efficiently. Blood backs up in the veins, and the resulting pressure pushes fluid into the tissues of the legs, ankles, and feet. The swelling tends to affect both legs equally and often gets worse toward evening.
Kidney disease reduces your body’s ability to filter excess fluid and salt, so both accumulate in the blood and eventually leak into surrounding tissues. The swelling typically appears in the legs and around the eyes. When kidney damage is severe enough to cause large amounts of protein to spill into the urine (a condition called nephrotic syndrome), albumin levels drop. With less protein to pull fluid back into the bloodstream, swelling can become widespread.
Liver cirrhosis disrupts protein production in a similar way. The liver makes most of your blood’s albumin, so significant liver damage leads to fluid buildup in the abdomen and legs.
Medications That Cause Swelling
Several common medications list foot swelling as a side effect. Blood pressure drugs called calcium channel blockers are among the most frequent culprits. Amlodipine, nifedipine, and felodipine cause more swelling than other drugs in the same class because they relax arteries more aggressively, increasing pressure in the smallest vessels downstream.
Other drug categories known to cause swelling include:
- NSAIDs (ibuprofen, naproxen) because they cause your kidneys to retain salt and water
- Steroid hormones like prednisone
- Estrogen-containing medications including some birth control pills and hormone replacement therapy
- Diabetes medications in the thiazolidinedione class
The swelling from these drugs tends to be dose-related, meaning it gets worse at higher doses and often improves if the dose is lowered or the medication is switched. If you notice new swelling after starting a prescription, bring it up with your prescriber rather than stopping on your own.
Pregnancy Swelling vs. Preeclampsia
Some degree of foot and ankle swelling is normal during pregnancy, particularly in the third trimester. Increased blood volume and hormonal changes make fluid retention almost unavoidable.
What’s not normal is sudden, severe swelling, especially in the face and hands. This can signal preeclampsia, a serious pregnancy complication defined by high blood pressure and signs of organ stress. Other warning signs include severe headaches, vision changes like blurriness or light sensitivity, pain under the ribs on the right side, shortness of breath, and nausea or vomiting that appears for the first time late in pregnancy. Preeclampsia requires immediate medical attention because it can progress rapidly.
Infection
A skin infection called cellulitis is a common cause of sudden swelling in one foot or lower leg. Bacteria enter through a small cut, crack, or insect bite and trigger an inflammatory response. The infected area becomes warm, red, swollen, and tender. At least two of those four signs are typically present.
Cellulitis can escalate quickly. A fever above 100.4°F alongside the swelling and redness suggests the infection may be spreading into the bloodstream and needs urgent treatment.
Blood Clots
Swelling that appears suddenly in only one leg is the classic warning sign of a deep vein thrombosis, a blood clot forming in a deep vein, usually in the calf or thigh. Along with the swelling, you may notice pain or tenderness that worsens when you stand or walk, warmth over the affected area, and skin that looks reddish or discolored.
A DVT is dangerous not because of the swelling itself, but because the clot can break free and travel to the lungs. That complication, called a pulmonary embolism, causes sudden shortness of breath, chest pain, and can be life-threatening. One-sided leg swelling with pain or warmth warrants same-day medical evaluation.
Managing Everyday Swelling
For swelling related to gravity, prolonged sitting, or mild venous insufficiency, a few strategies make a real difference. Elevating your feet above heart level for 15 to 20 minutes helps fluid drain back toward your core. Reducing salt intake limits how much water your body retains. And regular movement throughout the day, even in small doses, activates the calf muscles that act as a pump for your veins.
Compression stockings are one of the most studied tools for preventing and reducing lower leg swelling. Light compression in the 10 to 15 mmHg range is effective for people who sit or stand for long stretches at work. Moderate compression (15 to 20 mmHg) provides additional benefit, and 20 to 30 mmHg stockings are typically recommended for people with diagnosed venous insufficiency. Higher pressure doesn’t always mean better results. For most people with occupational swelling, light to moderate compression is enough.
When swelling is caused by an underlying condition like heart failure, kidney disease, or venous insufficiency, treating the root cause is what ultimately controls the fluid buildup. Compression and elevation help manage the symptom, but they don’t replace addressing the condition driving it.